1. Field of the Invention
The present invention relates to a life estimating method for a heater wire, a heating apparatus, a storage medium, and a life estimating system for the heater wire.
2. Background Art
As one type of semiconductor manufacturing apparatuses, a vertical type heating apparatus, in which a semiconductor wafer or wafers (hereinafter, referred to as “a wafer or wafers”) are processed in a batch, has been known. For example, this apparatus includes a vertical type reaction vessel constituting a processing chamber provided with a transfer port at its bottom end, a cylindrical heat insulating member provided to surround the reaction vessel, and a heater composed of a resistance heating member provided around an inner wall face of the heat insulating member. The apparatus is configured such that multiple sheets of wafers can be carried into the reaction vessel via the transfer port while they are held by a wafer holding tool in a shelf-like fashion. In this apparatus, oxidation, film forming or the like process can be provided to the wafers, by heating the interior of the reaction vessel up to a predetermined temperature by using the heater. As the resistance heating member, a heater wire consisting of, for example, an iron-tantalum-carbon alloy or the like, can be used, and the heater wire is formed into, for example, a coil, which is wound around the reaction vessel.
Upon providing an oxidation process, annealing, film forming based on chemical vapor deposition (CVD), or film forming based on molecular layer deposition (MLD) in which growth of a layer of a predetermined film is controlled at a molecular level, or the like, to the wafers, by heating the wafers by using the heater wire as described above, the interior of the reaction vessel is adjusted at a higher temperature, for example, approximately 900° C. Meanwhile, when the wafers are carried into the reaction vessel or carried out therefrom, the interior of the reaction vessel is adjusted at a relatively low temperature, for example, approximately 650° C., for suppressing growth of a naturally oxidized film on each wafer surface, or the like reason. Because the heater wire often undergoes such severe environments that it is repeatedly brought into higher and lower temperature states, it is sometimes disconnected in a shorter period of time, depending on processing conditions.
Once the disconnection of the heater wire occurs during the heating process, all of the wafers contained in the batch will be regarded as scraps (or defective goods), increasing the lost cost and wasting the time spent for the heating process. Therefore, a technique for estimating life of the heater wire, for example, for estimating a time of disconnection, is quite important for saving the production cost of the wafers and enhancing the yield.
In the past, various techniques have been proposed with respect to the life estimation for the heater wire. For example, in Patent Document 1 as listed below, the technique for estimating the time of disconnection is discussed, in which a resistance value of the heater wire is first monitored, and the time of disconnection is then estimated based on a transition of the resistance value. In addition, in Patent Document 2 as listed below, another approach for estimating the disconnection of the heater wire is described, in which electric power supplied to the heater wire during a period of time that the temperature is stabilized (or during a stabilized temperature period), is first measured for each application (i.e., carrying in of the wafers, heating process, and carrying out of the wafers), and a transition of the standard deviation of each application is then figured.
Patent Document 1: TOKUKAIHEI No. 5-258839, KOHO
Patent Document 2: TOKUKAI No. 2002-352938, KOHO
Of course, the interior of the reaction vessel cannot reach a predetermined temperature immediately after the supply of electric power to the heater wire is started. Namely, the temperature will be elevated gradually after the start of supply of the electric power until it reaches the predetermined temperature. In this case, the electric power supplied to the heater wire will be more stabilized after the temperature reaches the predetermined temperature than during the period of time that the temperature is elevated. Accordingly, in the past, as described above, electrical data, such as the resistance value or electric power, of the heater wire, has been collected during the so-called stabilized temperature period after the heater wire reached the predetermined temperature, so as to judge conditions of degradation or deterioration of the heater wire from the electrical data obtained during the stabilized temperature period.
Although the electrical data during the stabilized temperature period will exhibit significantly greater change when the heater wire is disconnected, it will not demonstrate such great change, irrespectively of conditions of the degradation of the heater wire, until it is completely disconnected. Therefore, especially in the case of estimating the disconnection before the heater wire is actually disconnected, it is quite difficult to detect a difference between the case in which there is no degradation of the heater wire and the case in which the degradation is progressing to some extent, thus making it difficult to appropriately estimate the life of the heater wire.
As described above, if the life of the heater wire cannot be appropriately estimated, the heater wire approaching the end of its life will be suddenly disconnected during the heating process, without being detected in advance to be in such a state. In addition, there is a risk that the heater wire not yet required to be exchanged would be estimated as one approaching the end of its life, and there is possibility that such a normal heater wire would be actually exchanged with another as well.
Even though the life of the heater wire can be estimated, if a point of time of the estimation is just before the end of its life, such estimation would be too late for preparing a new heater wire to be exchanged and/or make it difficult to prepare a maintenance schedule, in advance, for the exchange. Therefore, there is a risk that the heating apparatus must be stopped for a considerably long time, as such degrading the working ratio of the heating apparatus. Accordingly, it is preferred that the disconnection of the heater wire can be estimated at a possibly early point of time.